The rigidity of polymers can be enhanced by utilizing high levels or concentrations of polyfunctional crosslinking agents. Most crosslinked polymers can be manufactured by suspension or droplet polymerization where a liquid monomer mixture is dispersed or suspended in an immiscible liquid medium. Suspension polymerization produces spherical polymer particles that can be varied in size by a number of mechanical and chemical methodologies. These methodologies for making crosslinked polymers are well known and practiced in the art of suspension polymerization.
All of the crosslinking agents known in the art are chemical crosslinkers. There are many polyfunctional crosslinking agents in use, but the most prominent crosslinking monomer is divinylbenzene. Divinylbenzene is used to make insoluble, rigid polymers from acrylate esters, methacrylate esters, vinyl acetate, styrene, vinylnaphthalene, vinyltoluene, allyl esters, olefins, vinyl chloride, allyl alcohol, acrylonitrile, acrolein, acrylamides, methacrylamides, vinyl fluoride, vinylidene difluoride, etc. Almost any molecule carrying a carbon-carbon double bond (C.dbd.C) can be crosslinked and made rigid by copolymerization with divinylbenzene. Other crosslinking monomers are polyfunctional acrylates, methacrylates, acrylamides, methacylamides and polyunsaturated hydrocarbons.
Another crosslinking methodology known in the art is macroneting. In macroneting, a preformed polymer is swelled in a difunctional reactant and crosslinked with the assistance of a catalyst. An example of macroneting is the crosslinking of polystyrene swelled in a dihalohydrocarbon by the action of a Friedel-Crafts catalyst such as aluminum chloride or ferric chloride.
The beads of this invention differ from the prior art in that the polymeric beads are made rigid and nonelastic by the physical crosslinking of chain entanglement rather than by the chemical crosslinking of polyfunctional monomers.